Mobile devices, such as handheld personal computers and personal digital assistants (“PDAs”), are becoming increasingly popular ways to access the Internet. Unfortunately, the experience of users in accessing web pages using these mobile devices has been less than satisfactory. First, because these mobile devices have small display areas, it is difficult to effectively display in such a small display area a web page that is designed for a large display area. Second, because these mobile devices typically have a relatively slow communications link (e.g., via a cell phone network), it can take an unacceptably long time to download an accessed web page. Third, because the mobile devices have limited computing power, the rendering of a complex web page can also take an unacceptably long time.
To allow for the effective display of web pages on a small display area, some techniques have been developed to dynamically adapt web pages that are too large for a small display area. One such adaptation technique is “page splitting,” which attempts to divide a web page into blocks that can fit as a unit into a small display area. One such page splitting technique analyzes the position and shape of HTML elements of a web page to identify blocks. However, it can be difficult to identify blocks from low-level HTML tags in a way that preserves page structure and does not lose information. Moreover, such adaptation techniques can be computationally expensive, especially on a mobile device.
Some techniques have been developed to speed up delivery of dynamic web pages by caching such web pages either at a client or at a server. A dynamic web page is a web page that is generated dynamically when the web page is accessed. The content of such web pages can be tailored to the user or contain up-to-date information (e.g., stock quotes). Such caching techniques, however, typically cache on a page-by-page basis. As a result, when even a small portion of a dynamic web page is changed, the entire web page needs to be retrieved from the web server. Various strategies have been proposed to make the caching of web pages more effective. One such strategy designates fragments within a web page that represent a cacheable portion. Each fragment can have its own expiration time. Thus, only those fragments that have expired need to be retrieved from the web server, and fragments that have not expired can be retrieved from the cache. Although adaptation can be performed on a web page whose fragments have been refreshed, such adaptation is still time-consuming, especially for a mobile device.
It would be desirable to combine adaptation techniques with fragment-based caching techniques to improve the overall performance of accessing web pages via a mobile device. In particular, it would be desirable to avoid having to adapt an entire web page each time a fragment is refreshed and to take advantage of semantic information indicated by fragments when adapting a web page.